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I have a function generator, and I am outputting 100 mV peak to peak sine wave.
By making a circuit of resistances, I am trying to reduce the peak to peak voltage to 2 mV.
But I am getting noise in doing so.

enter image description here

Yellow coloured signal is the input signal, blue one is output signal. There is a faint blue colour band around the main signal.
I have to pass 2 mV signal to a device, is that noisy signal good enough to send to a device?
Or is ot just showing noise in the oscilloscope because the peak to peak voltage of output signal is very low?
I want to get a cleaner signal, is there any way to do so?

tobalt
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Manu
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    What's the resistance values for your voltage divider, exactly? (I can guess your scope impedance. Would be nice to know your choice in signal generator output. Was it 50 Ohm? Or something else?) – jonk Nov 09 '22 at 06:51
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    We don't know what your device is and if the resulting 2mV sine is too noisy for it. We also don't know what the device does with the input and what impedance the input has, and what resistor values you used, and what is the source impedance for sine wave. Add more information about your system. – Justme Nov 09 '22 at 06:51
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    How is wired your "system"? What resistors used? – Antonio51 Nov 09 '22 at 10:12
  • Please draw a schematic of your setup with values. – winny Nov 09 '22 at 13:10

2 Answers2

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The blue trace is amplified 200x more than the yellow trace (by the scope). It is natural that traces get noisy bands at the smallest ranges.

Make two additional comparisons:

  1. Short one of the scope inputs (so it reads 0 volts) and set it to the same range: Is the noise in the shorted trace smaller or same as the blue trace?

  2. set the signal generator to a low output level and read it also at the same range. How large is the noise here?

Now you make determine the dominant noise source:

  • If all traces have the same noise, then it is caused by your scope's amplification.
  • On the contrary, if the short trace has lower noise than the blue trace, it means there is excess noise beside your scope's amplification.
  • If the generator noise is ~50x as high as the blue trace, then that means that excess noise is caused by the function generator output. If the generator noise is smaller than 50x of the blue trace, it means that the excess noise is caused by your resistive divider.
winny
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tobalt
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0

The DPO 2024 has a 200MHz bandwidth. The scope probe/circuit can receive local RF interference (radio station).

The wide bandwidth will measure the thermal noise from the scope's input resistance as well as from the resistor network.

You should be able to restrict the bandwidth of the channel to about 60 MHz (depends on the scope) in the channel configuration menu.

The probes usually come with a "spring ground" accessory. See this SE question. The ground spring is often used to reduce ringing caused by the ground lead inductance resonating with the oscilloscope capacitance. By reducing the current loop area, the interference is also reduced.

winny
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RussellH
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